Synthesis, Characterization, and Photophysical Properties of Three Pt(II) Complexes Bearing Fluorescent Analogues of the Di-(2-pyridyl)methane Ligand

Article is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use. The MIT Faculty has made this article openly available. Please share how this access benefits you. Your story matters. RECEIVED DATE (to be automatically inserted after your manuscript is accepted if required according to the journal that you are submitting your paper to) Three new ligands of general formula [RNHCH(py) 2 ] (py = pyridine, R = tosyl, Ts-dpm; R = dansyl, Ds-dpm; R = 7-nitro-1,2,3-benzoxadiazole, NBD-dpm) have been synthesized and characterized. Reactions of these ligands with cis-[Pt(DMSO) 2 Cl 2 ] (DMSO = dimethyl sulfoxide) in methanol affords [Pt(Ts-dpm)Cl 2 ] (1), [Pt(Ds-dpm)Cl 2 ] (2), and [Pt(NBD-dpm)Cl 2 ] (3). The crystal structures of these complexes reveal bidentate coordination of the ligands to the Pt center with nonplanar chelate rings. Because of inequivalent substituents on the methine carbon atom of the ligands, distinct exo and endo iso-mers exist in the three complexes. X-ray analyses indicate that 1 crystallizes in the endo conformation, 2 in the exo conformation, and 3 as a mixture of the two conformers. The 1 H NMR and 195 Pt NMR spectra of the complexes display two sets of independent signals corresponding to the chemically inequivalent exo and endo conformers. The exo conformer was determined by 2D NMR spectroscopy to be thermo-dynamically favored for all three complexes. Density functional theory (DFT), time-dependent DFT 2 (TDDFT), and atoms in molecules (AIM) calculations were carried out for both conformers of 3 to investigate differences in their electronic structures and to explore intramolecular interactions. In the presence of dioxygen, 1 thermally decomposes at 60 °C to form several unidentified products. Compound 2 is thermally stable even in the presence of dioxygen and water, but upon light exposure decomposes to form a new Pt(II) species with a 195 Pt NMR shift of-2177 ppm. Compound 3 reacts both thermally and photochemically in the presence of dioxygen and trace amounts of water to form both 4-amino-7-nitro-2,1,3-benzoxadiazole (NBD-NH 2) and [Pt(dpk)Cl 2 ] (dpk = di-2-pyridylketone). Oxidation of 1 and 3 with H 2 O 2 in acetic acid affords a mixture of compounds, two of which contain dpm ligands bound in a tridentate manner to platinum.